Method for avoiding an internal coking of an injection hole for injection holes in a multi-hole injection valve

ABSTRACT

A method for avoiding an injector orifice internal coking of the spray orifices of a multi-orifice fuel injector of a direct injection internal combustion engine, e.g., of a motor vehicle, is provided. Fuel is injected into a combustion chamber of the internal combustion engine by multiple injections. The fuel is injected by a first main injection during the intake stroke and by a subsequent postinjection during the compression stroke before the ignition time. Thereby, during a long operation of the internal combustion engine, especially in a homogeneous operation, the injection time does not have to be continually increased in order to compensate for the increasingly shrinking cross section of the spray orifices.

FIELD OF THE INVENTION

The present invention relates to a method for operating a directinjection internal combustion engine, e.g., of a motor vehicle.

BACKGROUND INFORMATION

Direct injection internal combustion engines, in which fuel is injecteddirectly into the combustion chambers of the internal combustion engine,are known in the art. A direct injection internal combustion engine maybe operated in different operating modes, for instance, in a stratifiedoperation or a homogeneous operation. Stratified operation is usedespecially for small loads, whereas homogeneous operation comes into usefor greater loads on the internal combustion engine.

In stratified operation, the fuel is injected into the combustionchamber during a compression stroke of the internal combustion engine insuch a manner that, at the time of ignition, there is a fuel cloud inthe immediate surroundings of a spark plug. This injection may proceedin different manners. Thus, it is possible that the injected fuel cloudis at the spark plug already during, or immediately after the injection,and is ignited by it. It is also possible that the injected fuel cloudis supplied to the spark plug by a charge movement, and is only thenignited. In the case of both combustion methods there is no uniform fueldistribution, but rather a stratified charge.

Stratified operation may provide that, using a very slight quantity offuel, the smaller loads present are able to be performed by the internalcombustion engine. Greater loads, however, may not be handled bystratified operation.

In the homogeneous operation provided for such greater loads, the fuelis injected during an intake stroke of the internal combustion engine,so that a turbulence and thereby a distribution of the fuel is stillable to occur in the combustion chamber right away before the ignitionof the fuel/air mixture. To that extent, homogeneous operationcorresponds approximately to the operating manner of internal combustionengines in which, in the usual manner, fuel is injected into the intakepipe. If necessary, one may also switch over to homogeneous operationfor smaller loads.

In stratified operation, the throttle valve in the intake pipe leadingto the combustion chamber is opened wide, and combustion is controlledand/or regulated only by the fuel quantity to be injected. Inhomogeneous operation, the throttle valve is opened and closed as afunction of the required torque, and the fuel quantity to be injected iscontrolled and/or regulated as a function of the aspirated air mass. Inboth operating modes, that is, in stratified operation and inhomogeneous operation, the fuel quantity to be injected is alsocontrolled and/or regulated as a function of a multitude of additionaloperating variables towards an optimal value with respect to fuelsavings, exhaust gas reduction and the like. In this context, thecontrol and/or regulation is different for the two operating modes.

Also known in the art are internal combustion engines, in which fuel isinjected into the combustion chambers of the internal combustion engine,not by a single injection, but subdivided into several consecutiveinjections, especially by a main injection and a subsequentpostinjection. For example, an internal combustion engine is describedin published European Patent Application No. 0 971 104, in which thefuel is injected into the combustion chambers by a postinjection duringan exhaust stroke of the internal combustion engine, that is, clearlyafter the ignition time of a fuel/air mixture. The fuel quantityinjected by the postinjection arrives unburned in a catalytic converterof the internal combustion engine, and is ignited there. This leads toheating of the catalytic converter, so that temperatures required forthe regeneration of the catalytic converter may be achieved in thecatalytic converter.

Internal combustion engines having direct fuel injection, inpartial-load operation may not be driven steadily in thermodynamicallyoptimal, throttle-free, quality-controlled stratified operation. Inorder, for example, to ensure an effective fuel tank venting or anefficient regeneration of a nitrogen oxide (NO_(x)) catalytic converter,at certain time intervals (depending on the engine speed and the loadstate of internal combustion engine), a throttling of the intake air ofinternal combustion engine and a stoichiometric (ë=1) orsubstoichiometric (ë<1) fuel/air ratio connected therewith has to beset. As soon as the air intake supply is throttled, the fuel has to beinjected during the intake stroke and not—as in the (throttle-free)stratified charge operation—during the compression stroke. The internalcombustion engine then behaves, with respect to fuel usage and exhaustgas emission, like a conventional internal combustion engine havingmanifold injection.

It is known from other systems that, during the special functionsdescribed above, fuel tank venting, catalytic converter regeneration orothers, one may inject the fuel, within the scope of a one-timeinjection in the intake stroke. Displacing the injection time into thecompression stroke, in conjunction with extreme air intake throttling,causes very great soot emission, and is therefore not used in practice.

However, when the internal combustion engine is operated using extremeintake air throttling and stoichiometric mixture composition, the sprayorifices of the injectors coke up, with the effect that, after a certainrunning time of the internal combustion engine the injection time has tobe permanently increased, so that, at a predefined load, the fuel supplymay be held constant. By increasing the injection time tq it is achievedthat the time cross section ((dm/dt)*tq) for the fuel supply per workcycle remains unchanged.

Although the special functions for fuel tank venting and catalyticconverter regeneration are only activated for a short time, it isensured that the coking up of an injector valve, that is, a sprayorifice internal coking creating flow interference, has to be avoided inthis operating phase under all circumstances. Otherwise the injectiontime has to be increased above the limits of the application, after alonger operating duration.

Therefore the present invention effectively avoids injector orificeinternal coking of the spray orifices of a fuel injector, especially athigh air intake throttling and stoichiometric or substoichiometricmixture composition.

In order to achieve this, the present invention provides that thepredominant proportion of the entire fuel quantity is injected by themain injection, and a change in the torque developed by the internalcombustion engine is controlled and/or regulated exclusively via achange in the injection time during the main injection, and the fuel isinjected by the main injection and the subsequent postinjection beforethe ignition time of a fuel/air mixture.

SUMMARY

According to the present invention, by a subdivision of the injectionpulse into a plurality of injection pulses, injector orifice internalcoking of a fuel injector, e.g., of a multi-orifice fuel injector, mayeffectively be avoided. In addition, due to the split-up injection,combustion having a favorable efficiency sets in, which is shown by theexhaust gas temperature being clearly lower compared to when there issingle injection.

Combustion of a fuel/air mixture, at great underpressure and havingstoichiometric mixture composition, has great wall heat losses fromheating up the combustion chamber walls, and, consequently, also theinjection elements. Those regions are heated which are directly exposedto the combustion. On account of the heat of combustion, high-boilingdeposits are created at the inner walls of the spray orifices, which areno longer able to be completely burned. One may assume that, during thecombustion stroke the flame front engages the valve tip region, but thatthe combustion reactions in the spray orifice region are greatly sloweddown, since a rich mixture is present there, and the flame isextinguished at the cooler wall zones.

According to the present invention, a second and each additionalinjection of fuel into the combustion chamber is able to reduce thedeposits of the high-boiling fuel components on the inside of the sprayorifices of the fuel injector. On account of the second injection, theinside contour of the spray orifice region is blown free of the depositof fuel condensate that occurred before. Besides that, in response to asecond injection pulse, the fuel is pressed into the injector since, forexample, the fuel column in the fuel injector has to be injected againstthe compression pressure in the combustion chamber. This causes asaturated wall deposit of the fuel which does not have separationtendencies, whereby heat convection and valve inside cooling are greatlyimproved, and the separation of the fuel into highly volatile anddifficultly volatile fuel components is prevented. The fuel is injectedwith its additives almost completely into the combustion chamber. Due tothe suppressed separation, no partially reacted combustion residues thenform on the inside of the spray orifices. According to an exemplaryembodiment of the present invention, it is provided that, during thepostinjection, exactly so much fuel is injected that a valve needle ofthe fuel injector just still touches a lift stop, and thereafterimmediately closes again. Thereby, the quantity of the postinjection istightly limited time-wise. For this reason, a change in the torquedeveloped by the internal combustion engine is controlled and/orregulated exclusively via a change in the injection time during the maininjection.

According to an exemplary embodiment of the present invention, it isprovided that the main injection be performed during an intake stroke ofthe internal combustion engine, and the at least one postinjection beperformed during a compression stroke of the internal combustion engine.The main injection may be released as early as shortly after thegas-exchange-OT (top dead center), and should be concluded at the latestshortly before the successive UT (bottom dead center). The injectionposition of the main injection depends first of all on the shape of thecombustion chamber. Into combustion chambers including characteristicpiston recesses, injection may be made shortly after the gas-exchangetop dead center, since the piston-recess edge (uncritical with respectto washing out motor oil) and less so the cylinder wall are wetted, andin addition more time is available for mixture preparation. However, incombustion chambers including flat pistons, one may inject in the rangeof the top piston speed, since in this phase the aspirated air reachesits greatest flow speed, and thus the mixing of fuel and air would bemost intensive.

According to an exemplary embodiment of the present invention, the maininjection is made during a maximum speed of a piston of the internalcombustion engine, the piston marking the boundary of a combustionchamber of the internal combustion engine into which fuel is injected.The area around the main injection may lie around 270° KW (crankshaftangle) before the ignition top dead center.

The at least one postinjection is made after a predefinable compressionpressure level is reached in a combustion chamber of the internalcombustion engine into which fuel is injected. In addition to that, thepostinjection should occur shortly before the ignition time. Theearliest possible beginning of injection for the postinjection thusdepends also on the absolute value of the current cylinder pressure. Thepostinjection may be performed at an absolute air intake pressure ofabout 400 mbar and a compression pressure level in one combustionchamber of >2 bar. The data are exemplary for an operating result. It isimportant that the second injection occur after the mixture from thefirst injection has already condensed due to the increase in thecompression pressure.

The method according to the present invention may be used for avoidinginjector orifice internal coking of spray orifices of fuel injectors inan internal combustion engine.

The present invention also relates to a computer program that issuitable for performing the method according to the present inventionwhen the program is executed on a computing element, e.g., on amicroprocessor. The computer program may be stored on a storage element,e.g., on a flash memory.

The method according to the present invention may be implemented in theform of a memory element which is provided for a control unit of adirect injection internal combustion engine, e.g., in a motor vehicle.In this context, a computer program that is executable on a computingelement, e.g., on a microprocessor, and is programmed for performing themethod according to the present invention, is stored on the memoryelement. In this case, the present invention is therefore implemented bymanner of a computer program stored on the storage element, so that thisstorage element provided with the computer program constitutes thepresent invention in the same manner as the method for whoseimplementation the computer program is suitable. In particular, anelectrical storage medium, for example, a read-only memory, arandom-access memory, or a flash memory, may be used as the memoryelement.

According to another exemplary embodiment of the present invention, thecontrol unit controls the fuel injector in such a manner that the fuelinjector injects the predominant proportion of the entire fuel quantityto be injected, by the main injection, and the control unit controlsand/or regulates a change in the torque developed by the internalcombustion engine exclusively via a change in the injection time duringthe main injection, the control unit controlling the fuel injector insuch a manner that the fuel injector injects the fuel by the maininjection and the at least one subsequent postinjection before theignition time of a fuel/air mixture.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a direct injection internal combustion engine in which themethod according to the present invention is able to be applied.

FIG. 2 shows a diagram illustrating the comparison of soot emissions inresponse to different injections of fuel into a combustion chamber of aninternal combustion engine.

FIG. 3 shows a diagram illustrating the comparison of hydrocarbonemissions in response to different injections of fuel into a combustionchamber of an internal combustion engine.

FIG. 4 shows a diagram illustrating the comparison of exhaust gastemperatures in response to different injections of fuel into acombustion chamber of an internal combustion engine.

FIG. 5 shows a plot of a combustion pressure in a combustion chamber ofan internal combustion engine in response to an air intake pressure of400 mbar and an engine speed of 1800 rpm.

FIG. 6 shows a diagram illustrating the comparison of the injectiontimes in response to a constant fuel quantity to be injected fordifferent fuel injections.

DETAILED DESCRIPTION

FIG. 1 shows an internal combustion engine 1 of a motor vehicle, inwhich a piston 2 may be moved back and forth in a cylinder 3. Cylinder 3is provided with a combustion chamber 4, whose boundary is marked by,among other things, piston 2, an intake valve 5, and an exhaust valve 6.An intake manifold 7 is connected to intake valve 5, and an exhaust pipe8 is connected to exhaust valve 6.

In the region of intake valve 5 and of exhaust valve 6, there projectinto combustion chamber 4 a fuel injector 9 (a so-called injector)configured as a multi-orifice fuel injector and a spark plug 10. Fuel isable to be injected into combustion chamber 4 via injector 9. The fuelin combustion chamber 4 may be ignited by spark plug 10.

A rotatable throttle valve 11, through which air may be supplied tointake manifold 7, is accommodated in intake manifold 7. The quantity ofsupplied air is a function of the angular setting of throttle valve 11.In exhaust pipe 8 a catalytic converter 12 is accommodated, which isused for cleaning the exhaust gases created by the combustion of thefuel.

Piston 2 is set into back and forth motion by combustion of a fuel/airmixture in combustion chamber 4, which is transmitted to a crank shaft(not shown) and exerts a torque upon it.

A control unit 13 receives input signals 14 representing operatingvariables of internal combustion engine 1 measured by sensors. Forinstance, control unit 13 is connected to an air mass sensor, a lambdasensor, an engine speed sensor or the like. Moreover, control unit 13 isconnected to an accelerator sensor which generates a signal thatindicates the setting of an accelerator operated by the driver, and thusgives the torque that is called for. Control unit 13 generates outputsignals 15, using which the behavior of internal combustion engine 1 maybe influenced, via actuators or setters. For instance, control unit 13is connected to fuel injector 9, spark plug 10 and throttle valve 11, orthe like, and generates the signals required for their control.

Among other things, control unit 13 is provided for controlling and/orregulating the operating variables of internal combustion engine 1. Forexample, the fuel mass (via injection time tq) that is injected by fuelinjector 9 into combustion chamber 4, and the point in time of the fuelinjection are controlled and/or regulated by control unit 13, e.g., withrespect to a low fuel usage, a low exhaust gas emission and/or a lownoise emission. To this end, control unit 13 is equipped with amicroprocessor 16, which, in a storage medium 17 that is, for example,developed as a flash memory, has a computer program stored, that issuitable for execution of the control and/or regulation. For theexecution of the computer program stored in storage medium 17, it istransmitted as a whole, or as instructed, via a data transmissionconnection 18 to microprocessor 16.

Internal combustion engine 1 from FIG. 1 is able to be operated in aplurality of different operating settings. Thus, it is possible tooperate internal combustion engine 1 in an homogeneous operation, astratified operation, a homogeneous lean operation or the like.

In homogeneous operation, the fuel is injected during an intake strokeby fuel injector 9 directly into combustion chamber 4 of internalcombustion engine 1. On account of the relatively early injection, thefuel is made strongly turbulent right up to ignition, so that, incombustion chamber 4 a fuel/air mixture is created that is homogeneous.In this context, the torque to be produced is set by control unit 13 viathe setting of throttle valve 11. In homogeneous operation, theoperating variables of internal combustion engine 1 are controlledand/or regulated in such a manner that ë (the ratio of air quantitysupplied to the fuel mass supplied) is equal to one. Homogeneousoperation is used especially at full load.

Homogeneous lean operation corresponds to a great extent to homogeneousoperation, however, ë is set to a value >1.

In stratified operation, the fuel is injected during a compressionstroke by fuel injector 9 directly into combustion chamber 4 of internalcombustion engine 1. Accordingly, at ignition by spark plug 10, nohomogeneous mixture is present in combustion chamber 4, but rather afuel stratification. Apart from requirements such as an exhaust-gasrecirculation and/or a gas tank venting, throttle valve 11 may becompletely open, and internal combustion engine 1 may accordingly beoperated in an unthrottled manner. The torque to be produced is set instratified operation largely via the fuel mass ((dm/dt)*tq) injectedinto combustion chamber 4. Internal combustion engine 1 may be operatedin stratified operation, e.g., when idling and at partial load.

One may switch over between the types of operation named of internalcombustion engine 1. Such switchovers are performed by control unit 13.

Internal combustion engines 1 having direct fuel injection, inpartial-load operation may not be driven steadily in thermodynamicallyoptimal, throttle-free, quality-controlled stratified operation. Inorder, for example, to ensure effective fuel tank venting or anefficient regeneration of a nitrogen oxide (NO_(x)) catalytic converter12, at certain time intervals (depending on the engine speed and theload state of internal combustion engine 1), a throttling of the intakeair of internal combustion engine 1 and a stoichiometric orsubstoichiometric (ë<1) fuel/air ratio connected therewith has to beset. As soon as the air intake supply is throttled, the fuel has to beinjected during the intake stroke and not—as in the (throttle-free)stratified charge operation—during the compression stroke. Internalcombustion engine 1 then behaves, with respect to fuel usage and exhaustgas emissions, like a conventional internal combustion engine havingmanifold injection.

During operation of internal combustion engine 1 using extreme intakeair throttling and stoichiometric mixture composition, the sprayorifices of fuel injector 9 coke up, it is true, e.g., in response tothe injection of fuel during the intake stroke, with the effect that,after a certain running time, injection time tq has to be increasedpermanently by control unit 13, in order to be able to hold fuel supplyat a predefined load constant. The time cross section ((dm/dt*tq) forthe fuel supply per work cycle thus remains unchanged.

Even though the special functions such as gas tank venting or catalyticconverter regenerating are activated for only a short time period, ithas to be ensured that an injector orifice internal coking of the sprayorifices of fuel injector 9 and a therewith connected flow rateinterference are avoided under all circumstances, since otherwiseinjection time tq has to be increased above the application limits overa longer operating period.

According to the present invention, a method for avoiding injectororifice internal coking of the spray orifices of fuel injector 9 isprovided, in which the fuel is injected by multiple injection,especially by a double injection subdivided into a first main injectionand a subsequent postinjection, into combustion chamber 4 of internalcombustion engine 1. Thereby, injector orifice internal coking may beeffectively prevented, especially at high air intake throttling andstoichiometric or substoichiometric mixture composition.

In the main injection, the predominant proportion of the entire fuelmass to be injected is injected, whereas, during postinjection, only somuch fuel is injected that a valve needle of fuel injector 9 just stilltouches a lift stop, and thereafter closes again immediately. Therebythe quantity of the postinjection is tightly limited time-wise. Apossible change in the torque developed by the internal combustionengine is therefore controlled and/or regulated exclusively via a changein injection time tq during the main injection.

The best results are achieved, i.e. injector orifice internal coking isbest able to be prevented if the main injection is performed during anintake stroke of internal combustion engine 1 and the postinjection isperformed during a compression stroke of internal combustion engine 1.The main injection may be released as early as shortly after thegas-exchange-OT (top dead center), and should be concluded at the latestshortly before the successive UT (bottom dead center). The center ofmass of the main injection may be shifted into the region of maximumspeed of piston 2 by approximately 270° KW (crankshaft angle) beforeignition dead center. The injection position of the main injectiondepends first of all on the shape of combustion chamber 4. Intocombustion chambers including characteristic piston recesses, injectionmay be made shortly after the gas-exchange top dead center, since thepiston recess edge (uncritical with respect to washing out motor oil)and less so the wall of cylinder 3 are wetted, and in addition more timeis available for mixture preparation. In combustion chamber 4 includingflat pistons 2, one may inject in the range of the top piston speed ofpiston 2, since in this phase the aspirated air reaches its greatestflow speed, and thus the mixing of fuel and air would be most intensive.

The injection quantity of the postinjection is deposited in combustionchamber 4, between the achieving of a predefinable compression pressurelevel in combustion chamber 4, and shortly before the time of ignitionof the fuel/air mixture. The earliest possible beginning of injection ofthe postinjection thus depends on the amount of a certain cylinderpressure at the time of the beginning of injection.

FIG. 2 shows a diagram having soot emissions for different kinds of fuelinjection. The degree of soot emission may be given in FSN (filter smokenumber). It may be clearly noted that the least soot emission occurs fora single injection pulse during the suction stroke (ti-Sh). Asubstantially higher soot emission occurs, on the other hand, inresponse to a single injection pulse during the compression stroke(ti-Vh). Upon subdivision of the injection pulse into a main injectionpulse and a postinjection pulse, in accordance with the presentinvention (ti-2fach), a soot emission occurs which, to be sure, issomewhat greater than the soot emission in response to a singleinjection pulse during suction stroke (ti-Sh), but clearly below thesoot emission of a single injection pulse during compression stroke(ti-Vh). This shows that the method according to the present invention,for avoiding injector orifice internal coking, results in almost noincrease in soot emission.

FIG. 3 shows a diagram having hydrocarbon (HC) emissions for variouskinds of fuel injection. It may be clearly seen that the least HCemissions occur in response to a single injection pulse duringcompression stroke (Ti-Vh), and the largest HC emissions occur inresponse to a single injection pulse during suction stroke (ti-Sh). Inresponse to a subdivision of the injection pulse into a main injectionpulse and a postinjection pulse, according to the present invention(ti-2fach), it is true that higher HC emissions occur than in responseto a single injection pulse during compression stroke (ti-Vh), but lowerHC emissions than in response to an injections pulse during suctionstroke (ti-Sh). Thus the method according to the present invention leadsto the avoidance of injector orifice internal coking and also to notexcessively high HC emissions.

FIG. 4 shows a diagram having exhaust gas temperatures T for variouskinds of fuel injection. It may be clearly recognized that by far thehighest exhaust gas temperatures of about 675° C. occur in response to asingle injection pulse during compression stroke (ti-Vh). Somewhatlesser exhaust gas temperatures in the range of about 635° C. occur inresponse to a single injection pulse during suction stroke (ti-Sh). Byfar the lowest exhaust gas temperatures in the range of about 615° C.,however, appear in response to an injection pulse subdivided into a maininjection pulse and a postinjection pulse according to the presentinvention (ti-fach). The low exhaust gas temperatures point to a morecomplete combustion of the fuel in combustion chamber 4, and therewithto a high efficiency.

FIG. 5 shows a combustion pressure curve in combustion chamber 4, for anintake pipe pressure of about 400 mbar and a speed of internalcombustion engine 1 of about 1,800 rpm as a function of the angularposition of the crankshaft (° KW). The beginning of injection of themain injection was approximately 280° KW before ignition top dead center(0° KW). The injection time of the main injection amounted to about 1.3ms. The beginning of injection of the postinjection is approximately 55°KW before ignition top dead center. In response to an ignition time tqof the postinjection of about 0.9 ms, the end of injection of thepostinjection is about −45° KW before ignition top dead center. Acommon-rail pressure prevailing in a fuel metering system of internalcombustion engine 1 was approximately 120 bar for the combustion curveshown in FIG. 5. Injection time t_(z) is approximately at 30° KW beforeignition top dead center.

FIG. 6 shows the curves of injection times for different kinds of fuelinjection at constant engine load. Injection time tq that is to be setby control unit 13 is a measure of the degree of the injector orificeinternal coking. The more the spray orifices of fuel injector 9 areclogged with deposits, the longer injection time tq has to be selected,in order to inject the same fuel mass into the reduced spray orificediameter. The curve of injection time tq for a single injection pulseknown from other systems is shown in a dashed line in FIG. 6. Theinjection beginning is approximately 280° KW before the ignition topdead center. It may be clearly recognized that injection time tqincreases, during the course of an approximately 15 hour operating time,from a beginning reading of 1.7 ms to about 2.6 ms after 15 hoursduration of the experiment. The curve of injection time tq for themethod according to the present invention, in which the fuel injectionis subdivided into a main injection and a postinjection, is shown by asolid line. The beginning of the main injection is at about 280° KW, andthe beginning of the postinjection is at 55° KW before ignition top deadcenter. In response to an injection pulse subdivided into a maininjection pulse and a postinjection pulse, injection time tq remainsnearly constant. During an operating duration of about 18 hours,injection time tq went up only a very little from about 2.2 ms to about2.3 ms, after 18 hours. In FIG. 6, Nh denotes the valve lift of fuelinjector 9, which was selected the same size at 0.1 mm.

The subdivision of an injection pulse into a main injection pulse and apostinjection pulse is not only used to avoid the spray orifice internaldeposits, but also leads to stabilization of combustion in combustionchamber 4. If injection is made exclusively in suction stroke (ti-Sh),HC emission (cf FIG. 3) increases, accompanied by greater fluctuationsin the combustion pressure. If the injection occur exclusively in thecompression stroke (ti-Vh), soot emission rises (cf FIG. 2) and after acertain running time, shunting forms at spark plug 10 having all sortsof undesired side effects, such as ignition misfires, because theinsulating ceramic is contaminated with soot.

With the aid of the injection divided into two parts, according to thepresent invention (ti-2fach), a good compromise could also be found withrespect to the problem just mentioned, to be sure, having a moderateincrease in soot, but reduced HC emission, in conjunction with a morestable long time running behavior compared to single injection duringsuction stroke (ti-Sh).

By endoscopy exposures in combustion chamber 4, serious differences arerecognizable in the forming of the injection jets between the injectionin suction stroke (ti-Sh) and the injection in compression stroke(ti-Vh). Due to the great underpressure in intake pipe 7, the fuelexperiences intensive evaporation (sucking out of the spray orifices offuel injector 9) during the injection in intake stroke (ti-Sh). Thisfuel evaporation already occurs on the inside of fuel injector 9, inregions where the vapor pressure is undershot, conditioned upon theunderpressure in cylinder 3.

In the subsequent compression phase, the fuel vapor condenses anddeposits on the inner walls of the spray orifices of fuel injector 9.The combustion with strong underpressure and stoichiometric mixturecomposition has great wall temperature losses by heating up the walls ofcombustion chamber 4, and consequently also of the injection elements,above all of those regions which are directly submitted to thecombustion. On account of the heat of combustion, high-boiling depositsare finally created at the inner walls of the spray orifices, which areno longer able to be completely burned. In the combustion phase theflame front engages the tip region of fuel injector 9; however, thecombustion reactions in the spray orifice region are greatly sloweddown, since there a rich mixture is present (wall wetting by thecondensate) and the flame is extinguished at the cooler wall zones.

On account of the second injection, before ignition time tz within themeaning of the present invention, the inside contour of the sprayorifice region is blown free of the deposit of fuel condensate thatoccurred before.

In addition, in response to the second injection pulse, the fuel is nolonger sucked out of fuel injector 9, by downwards moving piston 2(underpressure) but is, on the contrary, more likely pressed into fuelinjector 9 by piston 2's upward motion (overpressure). The fuel columnin fuel injector 9 has to be injected counter to the compressionpressure. Thereby, there occurs a saturated wall deposit of the fuel inthe spray orifices without tendencies to separate, heat convection andvalve internal cooling are greatly improved, and separation into highlyvolatile and difficultly volatile fuel components is prevented. The fuelis injected with its additives almost completely into combustion chamber4. On account of the suppressed separation, there is then also noformation of partially reacted combustion residues which deposit on theinner sides of the spray orifices.

1-15. (Canceled).
 16. A method for operating a direct injection internalcombustion engine of a motor vehicle, comprising: injecting a fuel by afuel injector in a main injection and a subsequent injection into acombustion chamber of the internal combustion engine; wherein the maininjection is a predominant proportion of an entire fuel quantityinjected in an injection cycle, and wherein a change in a torqueproduced by the internal combustion engine is regulated by a change ininjection time during the main injection, and wherein the fuel isinjected by the main injection and the subsequent injection before anignition time of a fuel/air mixture.
 17. The method of claim 16, whereina selected quantity of fuel is injected during the subsequent injectionso that a valve needle of the fuel injector still touches a lift stopand thereafter immediately closes again.
 18. The method of claim 16,wherein the main injection is performed during an intake stroke of theinternal combustion engine and the subsequent injection is performedduring a compression stroke of the internal combustion engine.
 19. Themethod of claim 16, wherein the main injection is performed during amaximum speed of a piston of the internal combustion engine, and whereinthe piston defines a boundary of the combustion chamber of the internalcombustion engine into which the fuel is injected.
 20. The method ofclaim 16, wherein the subsequent injection is made after a predefinedcompression pressure level is reached in the combustion chamber of theinternal combustion engine into which the fuel is injected.
 21. Themethod of claim 20, wherein the subsequent injection is performed at anabsolute pressure of about 400 mbars in an intake manifold to thecombustion chamber of the internal combustion engine into which the fuelis injected, and at a compression pressure level of over 2 bars in thecombustion chamber.
 22. The method of claim 16, whereby internal cokingof an injector orifice of a spray orifice of the fuel injector isprevented.
 23. A computer program having a sequence of program codesconfigured to be executed by a computing element, the program codescontrolling, when executed by the computing element, a direct injectioninternal combustion engine of a motor vehicle in accordance with amethod comprising: injecting a fuel by a fuel injector in a maininjection and a subsequent injection into a combustion chamber of theinternal combustion engine; wherein the main injection is a predominantproportion of an entire fuel quantity injected in an injection cycle,and wherein a change in a torque produced by the internal combustionengine is regulated by a change in injection time during the maininjection, and wherein the fuel is injected by the main injection andthe subsequent injection before an ignition time of a fuel/air mixture.24. A storage medium for storing a computer program for a control unitof a direct injection internal combustion engine of a motor vehicle, thecomputer program configured to be executed by a computing element of thecontrol unit, the computer program having program codes for controllingthe direct injection internal combustion engine of the motor vehicle inaccordance with a method comprising: injecting a fuel by a fuel injectorin a main injection and a subsequent injection into a combustion chamberof the internal combustion engine; wherein the main injection is apredominant proportion of an entire fuel quantity injected in aninjection cycle, and wherein a change in a torque produced by theinternal combustion engine is regulated by a change in injection timeduring the main injection, and wherein the fuel is injected by the maininjection and the subsequent injection before an ignition time of afuel/air mixture.
 25. The storage medium of claim 24, wherein thestorage medium includes at least one of a read-only memory, a randomaccess memory and a flash memory, and wherein the computing elementincludes a microprocessor.
 26. A control unit for a direct injectioninternal combustion engine of a motor vehicle, the internal combustionengine including at least one combustion chamber and a fuel injector,the control unit comprising: an arrangement configured to control thefuel injector so that the fuel injector injects into the at least onecombustion chamber of the internal combustion engine a main injectionand a subsequent injection of fuel; wherein the main injection is apredominant proportion of an entire fuel quantity injected in aninjection cycle, and the arrangement controls a change in a torqueproduced by the internal combustion engine by a change in an injectiontime during the main injection, and wherein the arrangement controls thefuel injector to inject the main injection and the subsequent injectionbefore an ignition time of a fuel/air mixture.